I first identify rare types (<20 occurrences) and identify the types they optimally should be grouped with. I usually combined types within not across ecoregions.
##
## RT1_Ireland and Northern Ireland RT1_Tundra
## 18 19
## RT10_The Caucasus RT12_Baltic province
## 3 2
## RT2_Borealic uplands RT2_The Caucasus
## 3 14
## RT3_Hellenic western Balkan RT3_The Caucasus
## 5 11
## RT5_Hellenic western Balkan RT6_Baltic province
## 13 2
## RT6_Borealic uplands RT6_Pyrenees
## 4 1
## RT6_The Caucasus RT7_Ireland and Northern Ireland
## 6 4
## RT7_Pyrenees RT7_The Caucasus
## 19 16
## RT8_Ireland and Northern Ireland RT8_Tundra
## 7 12
## RT9_Baltic province RT9_Pyrenees
## 4 3
## RT9_Taiga
## 2I keep the rare RT1-based types, as very large rivers are quite distinct (e.g. Borgwardt et al. 2019).
In the following I adress the rare types ordered by ecoregions.
It is very surprising to find rivers of the type RT12 Mediterranean temporary and very small so far in the north. I assume that this is an erroneous assignment. As we are only dealing with two segments, I remove them from the data. The rivers of types RT6 and RT9 are combined with those of the same geology and altitude but different size (i.e. RT7 and RT8)
Only a few stream segments at the very edge of our data fall within this ecoregion. I remove it from the data set.
Both rare types (RT2 and 6) are calcareous medium-large types. It would be a possibility to combine them into one. Given the low prevalence of each type though (3 and 4 instances), the combined type would still be rare. Hence I rather combine them with the respective small types.
As with the Baltic province, RT6 and RT9 are combined with RT7 and RT8.
The only instance of the RT9 type (mid-altitude siliceous very small small) drains in to RT5 (lowland siliceous very small small). We will hence consider them as one type.
The area covered by BRT and the Illies region “Tundra” is small. I add them to the borealic Uplands
Here we find the opposite situation to the Pyrenees and the Baltic province: RT7/8 are rare and RT 6/9 more common. The approach, however, remains the same. We combine the mid-altitude streams to one type per bedrock, irrespective of size.
In this ecoregion small lowland rivers are rare because they are mostly temporary and thus fall under RT12. I will combine RT3 and RT5 to Hellenic very small - small perennial lowland rivers.